Integrated humidity sensor

A compact humidity sensor with a capacitive sensor element and processing electronics, for measuring the relative humidity of air, was developed. By a systematic selection of materials for dielectrics and electrodes, signals with linear dependence on moisture and only small changes with temperature were obtained. The electronic circuits are based on pulse length modulation and are designed for digital display. Two alternatives were developed. The circuits with bipolar IC's were specially laid out with 20 mA output, while the CMOS circuits were designed to save energy. In both cases the output signals are evaluated by microcomputers. A specially formed case provides mechanical protection for the sensor element and moistureproof encapsulation of the circuits. The modules were developed for one fabrication stage and were given to consumers for testing.